Electric utilities are now grappling with the challenge of deregulation and competition at a time of relatively slow growth in electricity demands. While plans for huge power plants are being shelved because of high costs and environmental concerns, new customers must still be supplied with electrical power. Existing plants and transmission lines are simply becoming overwhelmed in some areas. Nuclear power plants are fast becoming economic dinosaurs.
One alternative to generating electrical power is called a “turbogenerator”, a small gas turbine engine combined on a common shaft with an electric generator. When a permanent magnet generator/motor is utilized, the combination is referred to as a permanent magnet turbogenerator/motor.
Intake air is drawn through the permanent magnet turbogenerator/motor by the gas turbine compressor which increases the pressure of the air and forces it into a recuperator which receives exhaust gases from the gas turbine. The recuperator preheats the air before it enters the gas turbine combustor where the preheated air is mixed with fuel and burned. The combustion gases are then expanded in the turbine which drives the compressor and the permanent magnet rotor of the permanent magnet turbogenerator/motor is mounted on the same shaft as the gas turbine and compressor. The expanded turbine exhaust gases are then passed through the recuperator before being discharged from the turbogenerator/motor.
A permanent magnet turbogenerator/motor generally includes a rotor assembly having a plurality of equally spaced magnet poles of alternating polarity around the outer periphery of the rotor or, in more recent times, a solid structure of samarium cobalt or neodymium-iron-boron. The rotor is rotatable within a stator which generally includes a plurality of windings and magnetic poles of alternating polarity. In a generator mode, rotation of the rotor causes the permanent magnets to pass by the stator poles and coils and thereby induces an electric current to flow in each of the coils. Alternately, if an electric current is passed through the stator coils, the energized coils will cause the rotor to rotate and thus the generator will perform as a motor.
A permanent magnet turbogenerator/motor can be utilized to provide electrical power for a wide range of utility, commercial and industrial applications. While an individual permanent magnet turbogenerator may only generate 24 to 50 kilowatts, powerplants of up to 500 kilowatts or greater are possible by linking numerous permanent magnet turbogenerator/motors together. Standby power, peak load shaving power and remote location power are just several of the potential utility applications which these lightweight, low noise, low cost, environmentally friendly, and thermally efficient units can be useful for.
In order to meet the stringent utility requirements, particularly when the permanent magnet turbogenerator/motor is to operate as a supplement to utility power, precise control of the permanent magnet turbogenerator/motor is required.